The disclosed invention relates to inkjet printing systems that employ replaceable consumable parts including ink cartridges, and more particularly to mechanisms for visibly indicating the amount of ink remaining in an ink cartridge.
An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes xe2x80x9cdot locationsxe2x80x9d, xe2x80x9cdot positionsxe2x80x9d, or xe2x80x9cpixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink.
Inkjet printers print dots by ejecting very small drops of ink onto the print medium, and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
A printhead of a thermal inkjet printer is commonly implemented as an integrated circuit printhead that includes a nozzle plate having an array of ink ejecting nozzles, a plurality of ink firing chambers adjacent respective nozzles, and a plurality of heater resistors adjacent the firing chambers opposite the ink ejecting nozzles and spaced therefrom by the firing chambers. Each heater resistor causes an ink drop to be fired from its associated nozzle in response to an electrical pulse of sufficient energy. The printhead is mounted in a printhead cartridge that includes one or more ink reservoirs. Each of such ink reservoirs can comprise a replaceable main reservoir, a non-replaceable main reservoir, or an internal reservoir that receives ink from a remote or xe2x80x9coff-axisxe2x80x9d ink supply located remotely from the printhead cartridge.
A consideration with inkjet printing is the usefulness of knowing that an ink supply has reached a predetermined low level, which would allow appropriate action to be taken so that printing operations can be performed with minimal disruption, and without waste of time and ink that would result if the ink supply is depleted during a print job. Also, a printhead may be damaged if operated without adequate ink for ejecting.
Various mechanisms have been devised to sense the level of ink in inkjet reservoirs. Commonly assigned U.S. Pat. No. 5,751,300 (Cowger et al.) discloses an ink level sensor used in a trailing tube printer. A pair of electrical leads are implanted in a body of foam, and the current between the leads indicates ink level. The detected ink level is used to operate a valve that controls the amount of ink allowed into the print cartridge. Commonly assigned U.S. Pat. No. 5,079,570 (Mohr et al.) discloses a binary fluidic indicator in a disposable print cartridge that use a small tube or other element formed on the ink tank of an inkjet print cartridge. The main ink tank of the print cartridge is filled with a porous material such as polyurethane foam, glass beads, felt pen fibers, capillary tubes, and rolled up plastic film. The small element that provides the optical ink level indication holds free ink that is not suspended in a capillary material. When the ink level drops to a certain level, the capillary material in the main ink tank draws the ink from the indicator, to thus provide a binary indication that the ink has dropped to a selected level. The indicator can be either human or machine readable. Commonly assigned U.S. Pat. No. 5,406,315 (Allen et al.) discloses an optical sensor that detects the temperature and ink level based on changes in the reflectivity of a phase change material adjacent to or within the pen body housing.
Despite the foregoing and other ink level detection and indicating mechanisms, there remains a need for an inexpensive and reliable system for indicating and/or detecting the level of ink in inkjet ink supplies.